This invention relates to an x-ray film cassette and, in particular, to an x-ray cassette having a buckler arrangement adapted to effect quick release of an x-ray film maintained within the cassette.
In the development of x-ray film handling systems equipment has been provided which allows the automatic loading and unloading of x-ray film into a cassette under daylight conditions. Such equipment frees the operator from the need to load and unload a film to and from a cassette in a dark room. Exemplary of such an automatic system is that disclosed in U.S. Pat. No. Re. 28,438 (Schmidt) assigned to the assignee of the instant invention. This reissue patent describes an x-ray film package for use with a daylight loading cassette of the type disclosed in U.S. Pat. Nos. 3,784,835 and 3,870,889 (both to Schmidt and both assigned to the assignee of the present invention). U.S. Pat. No. 3,715,087 (Schmidt) describes a device used for unloading cassettes of the last-mentioned patents under daylight conditions.
In operation, a film sheet is automatically loaded into the cassette which is operative to hold the film between two opposed substantially parallel x-ray intensifying screens during a period of patient exposure. Following exposure, the cassette is unloaded under the influence of gravity using a device as disclosed in the last-mentioned patent which is adapted to release one of the two cassette plates supporting the intensifying screens to thereby relieve the holding pressure from the film sheet and allow it to drop under the influence of gravity into a light-tight container.
For a variety of reasons, it is important that the time required for the film to drop from the cassette be maintained to within a reasonable maximum on the order of approximately seven seconds. It is believed to be most advantageous that the film drop time occupy on the order of two to three seconds. However, it has been found that in cassettes embodying the teachings of the above-referenced patents, the x-ray film exhibits a tendency to adhere to one of the intensifying screens even after the holding pressure is relieved therefrom. It has been attempted to overcome this problem through the use of cantilevered conical actuators disposed along the cassette edges which are actuated by an actuating cam assembly and pivot inwardly of the cassette to thereby edgewise engage the film sheet and buckle the same to define a gap between the sheet and the screen. The entry of air into the gap tends to equalize the pressure forces on both sides of the sheet to permit it to respond to the influence of gravity and drop from the cassette.
It has been found, however, that the conical bucklers of the prior art work most effectively when the x-ray film used in the cassette exhibits no inherent curl or when the curled film used in the cassette is inserted such that the film concave side is placed against the movable back plate of the cassette. Due to the mechanics of film manufacture and storage, it is difficult to provide an x-ray film sheet which will not exhibit any inherent curl. Furthermore, it is unrealistic to assume that replacement film may be packaged with the curl in the same orientation from package to package or that the operator of the x-ray system will consistently mount packages of replacement film in such a way that the automatic dispensing equipment will load film sheets into a cassette with the concave portion of the sheet placed against the back plate of the cassette.
Accordingly, it is believed to be advantageous to provide an x-ray cassette having a buckler assembly which will consistently and reliably operate to buckle the film sheet from one of the supporting plates regardless of the orientation of the curled film sheet within the cassette.